The present invention is related to the field of lens protectors and especially centrifugal lens protectors.
Cameras are required to operate under many adverse conditions, including flying particles, such as rain and snow. Rain and snow may adhere to the camera lens, reducing image quality.
One well known solution is to place a spinning glass disc before the lens, so that all the particles are captured by the disc. The centrifugal force generated by the disc as it rotates throws the particles towards the circumference of the disc, where they fall off and/or otherwise stop interfering with the image.
U.S. Pat. No. 3,879,742 to Smith, the disclosure of which is incorporated herein by reference, has the disc mounted on a central axis, with a surveillance camera at an off-axis location relative to the disc.
U.S. Pat. No. 5,223,880 to Rapp, the disclosure of which is incorporated herein by reference, integrates the disc with a rotor of a magnetic motor, with a casing surrounding the disc being the motor housing.
U.S. Pat. No. 5,315,333 to Nash, the disclosure of which is incorporated herein by reference, provides a single motor coupled to the disc using a band. The disc is mounted on two lines of bearings. The lens protection device is mounted on the camera, to isolate lens from gyroscopic and vibration forces.
Australian application 9515074, the disclosure of which is incorporated herein by reference, describes another band-based system, in which the disc is said to rotate at between 2600 and 3000 RPM. It is suggested to use a curved or hydrophobic surface to assist in water removal. The motor can be powered using the camera battery pack or using a separate battery.
An aspect of some embodiments of the invention relates to symmetric application of force to a rotating transparent disc. In some embodiments of the invention, this symmetry reduces vibration, thus possibly reducing wear, noise and/or image degradation. In other embodiments, asymmetric application of force and/or support is provided, possibly also achieving the desired results of reducing noise, wear and/or vibration.
In some embodiments of the invention, the rotational force is applied directly to the disc by one, two, three, four or more motors located at the circumference of the disc. In some embodiments of the invention, a plurality of wheels are distributed around the disc, engaging and/or supporting the disc. Each such wheel may be motor driven or free turning. Optionally, but not necessarily, the wheels are evenly distributed around the circumference of the disc.
An aspect of some embodiments of the invention relates to balancing angular moments in a centrifugal lens protection device. In some embodiments of the invention, by balancing angular moments, the magnitude of gyroscopic effects are reduced substantially. In some embodiments of the invention, the weight, radius and/or rotations speed of the disc and the motors and/or wheels used to rotate the disc are matched, such that a total angular moment is close to zero. Thus, for example, the total weight of a wheel may be twice the weight of the disc, to make up for a larger radius of the disc. In some embodiments of the invention, all the rotations are in a single plane. In some embodiments of the invention, the wheels are located at 45xc2x0 to the horizontal and vertical axis, to better provide support for gyroscopic forces that are usually at about 45xc2x0 to the axis of motion. In a camera, the axis of motion is expected to be parallel or perpendicular to the gravitational field. Optionally, the wheels locations may be flattened out to be more horizontal, thus providing a 4:3 ration as is common in TV cameras.
An aspect of some embodiments of the invention relates to electrical and mechanical coupling of motors for driving a rotating disc. In some embodiments of the invention, the motor windings of two or more DC motors are connected in series, such that mechanical mismatch of their speeds is compensated for by electrical voltage redistribution between the motors, without requiring any additional circuitry. Thus, both motors engage the disc equally, substantially without any slippage, even if there is some difference in radius between the wheels coupled to the motors and/or the disc is uneven. Another possible advantage is the ability to use lower quality motors whose design characteristics are not tightly controlled, without the adverse effect of added noise and/or vibration.
An aspect of some embodiments of the invention relates to a calibration step for a rotating disc lens protection device. In some embodiments of the invention, the disc is mounted on a small plurality of wheels. During a calibration step, the disc is rotated and the eccentricity of the wheels relative to their axes is corrected, thus reducing wear, vibration and/or noise.
An aspect of some embodiments of the invention relates to a transparent disc being easily removable for cleaning without taking apart the lens protector. In some embodiments of the invention, the transparent disc can be snapped off the engaging wheels, once a rim cover is removed.
An aspect of some embodiments of the invention relate to a method of connecting wheels for gripping a transparent disc, on a motor for rotating the wheels. In some embodiments of the invention, the wheels are supported by a case, which may also support the motor. The axis of the motor is coupled to one or more wheels, via a plurality of damping pins, such as rubber pins. In some embodiments of the invention, a plastic molding is provided on the axis and this plastic molding is pinned to the wheels. In some embodiments of the invention, by not supporting the disc on the motor, vibration coupling between the motor and the disc are reduced by the indirect connection between them.
There is thus provided in accordance with some some embodiments of the invention, a lens protecting mechanism, comprising:
a transparent disc having a rim;
a plurality of wheels that engage and support the rim; and
at least one motor, coupled to at least one of said wheels to apply rotational force to said disc.
Optionally, said plurality of wheels comprises wheels having substantially identical mechanical properties. Alternatively or additionally, said plurality of wheels comprises four wheels. Alternatively or additionally, said al least one motor is coupled to said wheel using a rubber pin and wherein said motor does not substantially support said wheel against said disc. Alternatively or additionally, said wheels and said disc are constructed such that the angular inertia of the wheels substantially balances out the angular inertia of the disc. Alternatively or additionally, said wheels are arranged at substantially xc2x145xc2x0 to expected movement axis of a lens for which lens protection mechanism is adapted.
There is also provided in accordance with some some embodiments of the invention, a lens protection mechanism, comprising:
a rotating transparent disc; and
at least one counter-rotating object whose rotation substantially cancels out angular inertia caused by the rotation of the disc.
Optionally, said at least one counter-rotating object supports said disc. Alternatively or additionally, said at least one counter-rotating object applies rotational force to said disc.
There is also provided in accordance with some embodiments of the invention, apparatus for applying force to a rotating disc, comprising:
a first DC motor coupled to a first wheel for engaging said disc; and
a second DC motor coupled to a second wheel for simultaneously engaging said disc; and
wiring that connects said DC motors in series to a power source, such that the voltage distribution between the motors reflects the instantaneous rotational speed of each motor.
There is also provided in accordance with some embodiments of the invention, lens protection apparatus, comprising:
a rotating transparent disc;
at least one wheel, coupled to said disc and causing said disc to rotate; and
a rim on said disc snap-connecting said disc to said apparatus, such that said disc can be snapped off said apparatus by applying pressure to the disc. Optionally, said rim is snap-connected onto said wheel. Alternatively or additionally, said rim is resilient.